In hospitals, clinics and the like, it has been standard practice to sterilize various products such as gowns, drapes, sheets, dressings, and other articles, prior to use by placing them in an autoclave where they are subject to steam sterilization. This practice is necessary to avoid infection and prevent contamination from the use of such articles where the same are not in a sterile condition and is particularly important where the articles have previously been used in the care of other patients.
Ethylene oxide sterilization is typically utilized in hospitals or laboratories for treating articles, for example of plastic, paper, rubber or the like which cannot withstand heat sterilization. Sterilization is effected when ethylene oxide reacts with contaminating microorganisms to kill or inactivate them.
Medical materials such as gauzes, bandages, or absorbent cotton, or surgical instruments such as injectors, scalpels, or scissors have hitherto been used after they have been sterilized with dry heat, pressure steam, or by boiling, using a sterilizer in the hospital. However, they have recently been supplied to users (such as hospitals and medical practioners) in a hermetically sealed sterilized style after they have been completely sterilized in the factory of the manufacturer for medical and surgical materials, instead of sterilizing them immediately prior to their use in hospitals or the like.
As there is no visual way of determining whether a particular article is sterile or not, it has been the practice to use a color change indicator with the article when placed in the steam sterilization chamber. The color change indicator changes under the sterilizing conditions of the autoclave, thus indicated that the particular article or package has been passed through the sterilizing cycle. The indicator may be in the form of a ribbon or card to which a color change ink has been applied.
However, even though such indicators show whether the materials have been exposed to the sterilization process, there is no indication of whether the process was effective. One way of determining whether or not sterilizing has been effective is to include in the sterilizer a biological test strip. Such a strip consists of a selected level of organisms having a resistance greater than is likely to be encountered on the articles being sterilized. Organisms that are particularly difficult to destroy are selected as the control standard, e.g., Bacillus subtilis var. Niger and Bacillus stearothermophilus. After the sterilization cycle is completed, the strip is sent to the laboratory to determine if the organisms on the strip are dead thereby indicating sterilization effectiveness. While this method is reliable, it has the disadvantage of requiring several days or longer before the results are determined.
In addition to the time delay, the use of a biological test strip as an indicator has required a trained technician and clean room facilities for conducting the tests. In spite of all the precautions, using trained technicians and clean rooms, on occasion the tests are contaminated and false positives are obtained because of human error. The test must be considered positive and the product resterilized and retested causing delayed deliveries, increased costs, and the like.
However, the only way to be sure that the sterilization was effective is to run a biological test. Thus, improved tests are desired that would reduce or eliminate false positives and that would reduce or eliminate the requirement for trained technicians and or clean room environments for conducting the tests. Several attempts to provide a self-contained sterilization test have been described, for example, in U.S. Pat. Nos. 2,854,384; 3,068,154; 3,239,429; 3,346,464; 3,440,144 and 3,667,717. However, to date none of the solutions described previously has provided an entirely satisfactory self-contained sterilization effectiveness test indicator.